1.0 Field of the Invention
The present invention relates to motor vehicle cooling systems and, more particularly, to a charge air cooler/condenser sub-assembly for use in heavy vehicles such as trucks.
2.0 Related Art
Motor vehicles, including heavy vehicles such as trucks, utilize a radiator assembly to eliminate waste heat from the internal combustion engine of the vehicle. The waste heat is a by-product of the internal combustion process and must be removed to allow steady state operation of the vehicle powertrain system. The radiator assembly includes a frame mounted to the chassis of the motor vehicle and a radiator mounted to the frame and comprising a core, or heat exchanger, and inlet and outlet manifolds or header ranks which communicate with the core. The radiator core comprises a plurality of tubes and fins, typically disposed in alternating laterally extending rows, with the tubes communicating with the inlet and outlet tanks so as to provide a flowpath for an engine coolant fluid, particularly water or glycol. Ambient cooling air is forced across the tubes and fins during operation of the vehicle resulting in heat transfer from the heated engine coolant flowing inside the core tubes to the ambient air stream. The temperature of the coolant fluid is typically controlled by a thermostat but can still vary by 20.degree.-40.degree. F. during normal operation of the vehicle due to engine load, ambient conditions, altitude and vehicle speed. The mean temperature of the radiator is therefore not constant, while the temperature of the frame remains relatively constant, corresponding approximately to ambient temperature. Known radiator cores are typically rigidly mounted to the radiator frame, thereby failing to accommodate the differential expansion of the core and frame. For instance, in one known apparatus, the radiator frame includes upper and lower members, with each fixedly attached at opposite ends to the radiator inlet and outlet tanks, thereby causing the tanks to be structural load-carrying members. In some instances, this arrangement, coupled with the differential thermal expansion of the radiator core tubes and the frame, has resulted in tube distress, in the form of cracks, at a location proximate one of the tanks.
The engines of heavy vehicles such as trucks may be turbocharged and accordingly such vehicles may include a charge air cooler (CAC) for purposes of cooling the turbocharged engine intake air before the air enters the engine for the combustion process. The intake air is heated during the turbocharger compression process and must be cooled by the CAC to satisfy engine durability and performance requirements. The CAC typically includes inlet and outlet manifolds and a core assembly having a plurality of alternating tubes and fins, with ambient air forced across the tubes so as to cool the heated intake air flowing through the tubes during operation of the vehicle. The temperature of the tubocharged intake air varies widely as a function of engine load, ambient conditions, altitude and vehicle speed. Consequently, as with the radiator, the mean temperature of the CAC is not constant.
Heavy vehicles also typically include a refrigerant condenser assembly which receives high pressure, superheated refrigerant gas from the refrigerant compressor and condenses the gas into a high pressure liquid for expansion and cooling of the vehicle cab. The superheated vapor is first cooled to its saturation point at the existing operating pressure and is then condensed isothermally into the high pressure liquid. The high pressure liquid is then sub-cooled to a temperature below the condensing temperature. The temperatures within the condenser vary widely due to vehicle thermal load, engine speed, vehicle speed and ambient conditions.
Heat exchangers such as the radiator, CAC and condenser are surface area dependent, requiring substantial surface area to produce the required temperature reduction of the fluids being cooled. The radiator, CAC and condenser may be mounted in a parallel flow relationship, so as to maximize the airflow through each unit, as shown in FIG. 1 of U.S. Pat. No. 5,095,882, with respect to a radiator assembly and a CAC, or aftercooler. However, such a parallel flow arrangement is unnecessarily cumbersome, particularly in small engine compartments. Accordingly, in certain applications it is desirable to arrange the various heat exchangers in a stacked, or series flow arrangement. While this arrangement alleviates the spatial problem associated with the parallel flow mounting scheme, known systems of this type fail to accommodate the differential thermal expansion which may occur between each adjacent pair, of heat exchangers, due to the varying temperature profiles of the radiator, CAC, and condenser. For instance, the inventor is not aware of any known systems which accommodates differential thermal expansion between a condenser and a CAC mounted in series. Failure to accommodate this differential thermal expansion can result in relatively large thermal stresses, which in turn can cause premature component failures.